Methods for forming a silicon nitride film

ABSTRACT

Methods for forming a silicon nitride film by a plasma enhanced atomic layer deposition (PEALD) process are provided. The methods may include: providing a substrate into a reaction chamber; and performing at least one unit deposition cycle of a PEALD process, wherein a unit cycle comprises, contacting the substrate with a vapor phase reactant comprising a silicon precursor; and contacting the substrate with a reactive species generated from a gas mixture comprising a nitrogen precursor and an additional gas. Methods for improving the etch characteristics of a silicon nitride film utilizing a post deposition plasma treatment are also provided.

FIELD OF INVENTION

The present disclosure generally relates to methods for forming a silicon nitride film and particularly methods for depositing a silicon nitride film by performing at least one unit deposition cycle of a plasma enhanced atomic layer deposition process. The present disclosure also generally relates to methods for depositing a silicon nitride film and treating the silicon nitride film post-deposition with a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas.

BACKGROUND OF THE DISCLOSURE

In the field of semiconductor device technology, silicon nitride films may be utilized during the fabrication of semiconductor integrated circuitry. For example, silicon nitride films may be utilized as an insulating material during the fabrication of semiconductor device structures, such as, for example, transistors, memory cells, logic devices, memory arrays, etc.

Common silicon nitride film deposition processes require high temperature deposition, i.e., around 600° C. to 800° C., to attain the reaction between precursors such as dichlorosilane (DCS) and ammonia (NH₃). State of the art device structures may not be able to withstand such a high thermal budget, which may further result in a deterioration of device performance and may cause device integration problems.

An alternative solution to high temperature deposition processes may be to utilize a plasma to activate the precursors which may in turn allow for low temperature reactions and reduced deposition temperatures for silicon nitride films. For example, plasma enhanced atomic layer deposition (PEALD) processes may be utilized to deposit high quality, conformal, silicon nitride films.

However, the low density of reactive species generated by common nitrogen precursors utilized in silicon nitride PEALD processes may result in long plasma exposure times for high quality films. Accordingly, methods are desirable for increasing the population density of reactive species from the nitrogen precursors utilized in silicon nitride PEALD processes to reduce deposition time and substrate throughput.

SUMMARY OF THE DISCLOSURE

In accordance with at least one embodiment of the disclosure, a method for forming a silicon nitride film by a plasma enhanced atomic layer deposition (PEALD) process is provided. The method may comprise: providing a substrate into a reaction chamber; and performing at least one unit deposition cycle of a PEALD process, wherein a unit deposition cycle comprises: contacting the substrate with a vapor phase reactant comprising a silicon precursor; and contacting the substrate with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

The embodiments of the disclosure also include a method for forming a silicon nitride film, the method comprising: providing a substrate into a reaction chamber; depositing a silicon nitride film on a surface of the substrate; and contacting the silicon nitride film with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

For the purpose of summarizing the invention and the advantages achieved over the prior art, certain objects and advantages of the invention have been described herein above. Of course, it is to be understood that not necessarily all such objects or advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught or suggested herein without necessarily achieving other objects or advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed. These and other embodiments will become readily apparent to those skilled in the art from the following detailed description of certain embodiments having reference to the attached figures, the invention not being limited to any particular embodiment(s) disclosed.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

While the specification concludes with claims particularly pointing out and distinctly claiming what are regarded as embodiments of the invention, the advantages of embodiments of the disclosure may be more readily ascertained from the description of certain examples of the embodiments of the disclosure when read in conjunction with the accompanying drawing, in which:

FIG. 1 illustrates a process flow diagram illustrating an exemplary process for forming a silicon nitride film in accordance with the embodiments of the disclosure;

FIGS. 2A and 2B illustrate optical emission spectra (OES) from a number of exemplary plasmas in accordance with the embodiments of the disclosure;

FIG. 3 schematically illustrates an exemplary unit deposition cycle of a PEALD process for depositing a silicon nitride film according to the embodiments of the disclosure;

FIG. 4 illustrates the wet etch rate ratio (WERR) vs thermal oxide for various silicon nitride films deposited according to the embodiments of the disclosure;

FIG. 5 illustrates a process flow diagram illustrating an exemplary process for forming a silicon nitride film including a post-deposition plasma treatment process in accordance with the embodiments of the disclosure;

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Although certain embodiments and examples are disclosed below, it will be understood by those in the art that the invention extends beyond the specifically disclosed embodiments and/or uses of the invention and obvious modifications and equivalents thereof. Thus, it is intended that the scope of the invention disclosed should not be limited by the particular disclosed embodiments described below.

As used herein, the term “substrate” may refer to any underlying material or materials that may be used, or upon which, a device, a circuit or a film may be formed.

As used herein, the formula for the silicon nitride is generally referred to as SiN for convenience and simplicity. However, the skilled artisan will understand that the actual formula of the silicon nitride, representing the Si:N ratio in the film and excluding hydrogen or other impurities, can be represented as SiN_(x), where x varies from about 0.5 to about 2.0, as long as some Si—N bonds are formed. In some cases, x may vary from about 0.9 to about 1.7, from about 1.0 to about 1.5, or from about 1.2 to about 1.4. In some embodiments, silicon nitride is formed where Si has an oxidation state of +IV and the amount of nitride in the material may vary.

As used herein, the term “film” and “thin film” may refer to any continuous or non-continuous structures and material deposited by the methods disclosed herein. For example, “film” and “thin film” could include 2D materials, nanolaminates, nanorods, nanotubes, or nanoparticles or even partial or full molecular layers or partial or full atomic layers or clusters of atoms and/or molecules. “Film” and “thin film” may comprise material or a layer with pinholes, but still be at least partially continuous.

As used herein, the term “plasma enhanced atomic layer deposition” (PEALD) may refer to a vapor deposition process in which deposition cycles, preferably a plurality of consecutive deposition cycles, are conducted in a reaction chamber. Typically, during each unit deposition cycle a precursor is chemisorbed to a deposition surface (e.g., a substrate surface or a previously deposited underlying surface such as material from a previous PEALD cycle), forming a monolayer or sub-monolayer that does not readily react with additional precursor (i.e., a self-limiting reaction). Thereafter, reactive species generated by a plasma produced from one or more precursors may subsequently be introduced into or generated in the process chamber for use in converting the chemisorbed precursor to the desired material on the deposition surface. Further, purging steps may also be utilized during each unit deposition cycle to remove excess precursor and reactive species from the process chamber and/or remove excess reactant, reactive species and/or reaction byproducts from the process chamber after conversion of the chemisorbed precursor.

In the specification, it will be understood that the term “on” or “over” may be used to describe a relative location relationship. Another element or layer may be directly on the mentioned layer, or another layer (an intermediate layer) or element may be intervened therebetween, or a layer may be disposed on a mentioned layer but not completely cover a surface of the mentioned layer. Therefore, unless the term “directly” is separately used, the term “on” or “over” will be construed to be a relative concept. Similarly to this, it will be understood the term “under,” “underlying,” or “below” will be construed to be relative concepts.

The embodiments of the disclosure may include methods for forming a silicon nitride film by a plasma enhanced atomic layer deposition process and particularly methods for reducing the plasma exposure time period for forming high quality silicon nitride by utilizing reactive species generated by the plasma excitation of a gas mixture comprising a nitrogen precursor and an additional gas. The embodiments of the disclosure may also include methods for forming silicon nitride films with improved etch characteristics by exposing a silicon nitride film post-deposition to a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas.

Silicon nitride films have a wide variety of applications, such as in planar logic, DRAM, and NAND flash devices. More specifically, conformal silicon nitride thin films that display uniform etch behavior have a wide variety of applications, both in the semiconductor industry and also outside of the semiconductor industry. According to some embodiments of the present disclosure, various silicon nitride films and precursors and methods for depositing those films by plasma enhanced atomic layer deposition (PEALD) are provided. Importantly, in some embodiments, the silicon nitride films have a relatively uniform etch rate for both the vertical and horizontal portions, when formed on or over three-dimensional structures. Such three-dimensional structure may include, for example, FinFETs or other types of multiple gate FETs.

The embodiments of the disclosure may therefore include methods for forming a silicon nitride film by a plasma enhanced atomic layer deposition (PEALD) process, the method comprising: providing a substrate into a reaction chamber; and performing at least one unit deposition cycle of a PEALD process, wherein a unit deposition cycle comprises: contacting the substrate with a vapor phase reactant comprising a silicon precursor; and contacting the substrate with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

Therefore, in some embodiments of the disclosure, plasma enhanced atomic layer deposition (PEALD) processes are used to deposit SiN films. Briefly, a substrate or a workpiece is placed in a reaction chamber and subjected to alternatively repeated surface reactions. In some embodiments, SiN films are formed by repetition of a self-limiting ALD cycle. In some embodiments, each PEALD unit deposition cycle comprises at least two distinct phases. The prevision and removal of a reactant from the reaction space may be considered a phase.

In a first phase, a first reactant comprising a silicon precursor may be provided into the reaction chamber and may form no more than about one monolayer on the substrate surface. This reactant is also referred to herein as the “the silicon precursor,” “silicon-containing precursor,” or “silicon reactant” and may be, for example, a vapor phase reactant comprising a silicon halide.

In a second phase, a second reactant comprising a reactive species is provided and may convert the absorbed silicon precursor to silicon nitride. In some embodiments of the disclosure, the second reactant may comprise a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas. In some embodiments, the additional gas may comprise at least one of helium or neon and the gas mixture may be introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

An exemplary process 100 for depositing a silicon nitride film utilizing a plasma enhanced atomic layer deposition process is illustrated with reference to FIG. 1. The exemplary process 100 may comprise two phases, a first phase comprising contacting the substrate with a silicon precursor and a second phase comprising contacting the substrate with a reactive species generated from a plasma.

In more detail and with reference to FIG. 1, the exemplary process 100 may commence by means of a process block 110 which comprises, providing a substrate into a reaction chamber and heating the substrate to a suitable deposition temperature.

In some embodiments, the substrate may comprise one or more materials and material surfaces including, but not limited to semiconductor materials, dielectric materials, and metallic materials. For example, the substrate may include semiconductor materials, such as, but not limited to, silicon (Si), germanium (Ge), germanium tin (GeSn), silicon germanium (SiGe), silicon germanium tin (SiGeSn), silicon carbide (SiC), or a group III-V semiconductor material.

In some embodiments of the disclosure, the substrate may comprise a patterned substrate including high aspect ratio features, such as, for example, trench structures, vertical gap features, horizontal gap features, and/or fin structures. For example, the substrate may comprise one or more substantially vertical gap features and/or one or more substantially horizontal gap features. The term “gap feature” may refer to an opening or cavity disposed between opposing inclined sidewalls or two protrusions extending vertically from the surface of the substrate or opposing inclined sidewalls of an indentation extending vertically into the surface of the substrate, such a gap feature may be referred to as a “vertical gap feature.” In some embodiments, the vertical gap features may have an aspect ratio (height:width) which may be greater than 2:1, or greater than 5:1, or greater than 10:1, or greater than 25:1, or greater than 50:1, or even greater than 100:1, wherein “greater than” as used in this example refers to a greater distance in the height of the gap feature. The term “gap feature” may also refer to an opening or cavity disposed between two opposing substantially horizontal surfaces, the horizontal surfaces bounding the horizontal opening or cavity; such a gap feature may be referred to as a “horizontal gap feature.” In some embodiments, the horizontal gap features may have an aspect ratio (height:width) which may be greater than 1:2, or greater than 1:5, or greater than 1:10, or greater than 1:25, or greater than 1:50, or even greater than 1:100, wherein “greater than” as used in this example refers to a greater distance in the width of the gap feature.

In some embodiments, the substrate on which deposition is desired is loaded into a reaction chamber. In some embodiments, the reaction chamber may form a part of a cluster tool in which a variety of different processes in the formation of semiconductor device structures are carried out. In some embodiments, a flow-type reactor may be utilized. In some embodiments, a showerhead-type reactor may be utilized. In some embodiments, a space divided reactor may be utilized. In some embodiments, a high-volume manufacturing-capable single wafer PEALD reactor may be utilized. In other embodiments, a batch reactor comprising multiple substrates may be utilized. For embodiments in which a batch PEALD reactor is used, the number of substrates may be in the range of 10 to 200, or 50 to 150, or even 100 to 130.

In some embodiments, if necessary, the exposed surfaces of the substrate may be pretreated to provide reactive sites to react with the first phase of the PEALD process. In some embodiments, a separate pretreatment step is not required. In some embodiments, the substrate is pretreated to provide a desired surface termination, for example, by exposing the substrate surface to a pretreatment plasma.

In some embodiments of the disclosure, the substrate disposed within the reaction chamber may be heated to a desired deposition temperature for a subsequent cyclical deposition stage 105 of exemplary PEALD process 100 (FIG. 1). For example, the substrate may be heated to a substrate temperature of less than approximately 600° C., or less than approximately 550° C., or less than approximately 500° C., or less than approximately 450° C., or less than approximately 400° C., or less than approximately 350° C., or even less than approximately 300° C. In some embodiments of the disclosure, the substrate temperature during the exemplary plasma enhanced atomic layer deposition process 100 may be between approximately 300° C. and approximately 600° C.

In addition to controlling the temperature of the substrate, the pressure in the reaction chamber may also be regulated to enable deposition of a desired silicon nitride film. In some embodiments, regulating the pressure within the reaction chamber may also control the population density and the nature of the reactive species generated within the plasma (to be described in greater herein below). Therefore, in some embodiments, the pressure in the reaction chamber during the exemplary PEALD process 100 may be regulated at a pressure greater than 2000 Pascals, or greater than 3000 Pascals, or greater than 4000 Pascals, or greater than 5000 Pascals, or even greater than 6000 Pascals. For example, in some embodiments, the pressure within the reaction chamber during the exemplary PEALD process 100 may be regulated between 2000 Pascals and 6000 Pascals.

Once the temperature of substrate has been set to the desired deposition temperature and pressure in the reaction chamber has been regulated as desired, the exemplary process 100 may continue by means of a cyclical deposition stage 105 which may include providing one or more deposition gases to the reaction chamber, wherein deposition gases may include vapor phase reactants, purge gas, carrier gas, and a gas mixture utilized to generate a reactive species from a plasma.

In brief, in a first phase of the cyclical deposition stage 105, a silicon precursor may be “pulsed” into the reaction chamber, wherein the term “pulse” may be understood to comprise feeding a reactant into the reaction chamber for a predetermined amount of time. The term “pulse” does not restrict the length or duration of the pulse and a pulse may be any length of time. In some embodiments, in addition to a silicon precursor a gas mixture may be provided to the reaction chamber continuously during the cyclical deposition stage 105 of exemplary PEALD process 100. In some embodiments, the gas mixture may comprise both a gas mixture for generation of reactive species utilized during the second stage of the PEALD process 100 and may also be utilized as a purge gas to remove excess reactants, reactive species, and reaction byproducts from the reaction chamber.

In more detail, the cyclical deposition stage 105 of exemplary PEALD process 100 may continue by means of a process block 120 comprising, contacting the substrate with a vapor phase reactant comprising a silicon precursor.

In some embodiments, the silicon precursor may be provided first to the substrate. After an initial surface termination, if necessary or desired, a silicon precursor pulse may be supplied to the substrate. In accordance with some embodiments, the silicon precursor may be supplied to the reaction chamber along with a carrier gas flow. In some embodiments, the silicon precursor may comprise a volatile silicon species that is reactive with the surface(s) of the substrate. The silicon precursor pulse may self-saturate the substrate surfaces such that excess constituents of the silicon precursor pulse do not further react with the molecular layer formed by this process.

The silicon precursor pulse is preferably supplied as a vapor phase reactant. The silicon precursor gas may be considered “volatile” for the purposes of the present disclosure if the species exhibits sufficient vapor pressure under the process conditions to transport species to the substrate surface in sufficient concentration to saturate the exposed surfaces.

In some embodiments of the disclosure, the vapor phase silicon precursor may comprise a silicon halide precursor. For example, in some embodiments, the silicon precursor may comprise at least one of a silicon chloride precursor, a silicon iodide precursor, or a silicon bromide precursor. In some embodiments, the vapor phase silicon precursor may comprise a silicon iodide selected from the group comprising SiI₄, HSiI₃, H₂SiI₂, H₃SiI, Si₂I₆, HSi₂I₅, H₂Si₂I₄, H₃Si₂I₃, H₄Si₂I₂, H₅Si₂I, or Si₃I₈. In some embodiments, the vapor phase silicon precursor may comprise H₂SiI₂. More detailed information regarding vapor phase silicon halide precursors may be found in U.S. Pat. No. 9,564,309, filed on Jan. 29, 2014, entitled “SI PRECURSORS FOR DEPOSITION OF SIN AT LOW TEMPERATURES,” all of which is hereby incorporated by reference and made a part of this specification.

In some embodiments of the disclosure, the silicon precursor may be pulsed into the reaction chamber for a time period from about 0.05 second to about 5.0 seconds, or from about 0.1 seconds to about 3 seconds, or even about 0.2 seconds to about 1.0 seconds. In addition, during the contacting of the substrate with the silicon precursor, the flow rate of the silicon precursor may be less than 200 sccm, or less than 100 sccm, or less than 50 sccm, or less than 10 sccm, or even less than 2 sccm. In addition, during the contacting of substrate with the silicon precursor the flow rate of the silicon precursor may range from about 2 to 10 sccm, from about 10 to 50 sccm, or from about 50 to about 200 sccm.

After sufficient time for a molecular layer to adsorb on the substrate surface, excess silicon precursor may be removed from the reaction chamber. In some embodiments, the excess silicon precursor may be purged by stopping the flow of the vapor phase silicon precursor while continuing to flow a carrier gas, a purge gas, or a gas mixture, for a sufficient time to diffuse or purge excess reactants and reactant by-products, if any, from the reaction chamber. In some embodiments, the excess silicon precursor may be purged with aid of one or more inert gases, such as nitrogen, helium or argon, that may be flowing throughout the cyclical deposition phase 105 of exemplary PEALD process 100.

In some embodiments, the silicon precursor may be purged from the reaction chamber for a time period of about 0.1 seconds to about 10 seconds, or about 0.3 seconds to about 5 seconds, or even about 0.3 seconds to about 1 second. Provision and removal of the silicon precursor may be considered as the first or “silicon phase” of the exemplary PEALD process 100.

Upon completion of the purging the reaction chamber of excess silicon precursor and any reaction by-products, the cyclical deposition stage 105 of exemplary PEALD process 100 may continue with a second phase by means of a process block 130 comprising, contacting the substrate with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture may be introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

In the second phase, a second reactant comprising a reactive species generated from a plasma is provided to the substrate. In some embodiments, a nitrogen based plasma is produced from a gas mixture comprising a nitrogen precursor and an additional gas. In some embodiments, the nitrogen precursor may comprise at least one of nitrogen (N₂), ammonia (NH₃), hydrazine (N₂H₄), or an alkyl-hydrazine (e.g., tertiary butyl hydrazine (C₄H₁₂N₂). In some embodiments, the additional gas may comprise at least one of helium or neon and the gas mixture may be introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen gas greater than 4:1, or greater than 10:1, or greater than 15:1, or even equal to or greater than 20:1. In some embodiments, the flow rate ratio of the additional gas to nitrogen precursor into the reaction chamber may be between approximately 4:1 and approximately 20:1. For example, the percentage volume of the additional gas within the gas mixture may be greater than 70 percent, or greater than 75 percent, or greater than 80 percent, or greater than 85 percent, or even greater than 90 percent. In some embodiments, the percentage volume of the additional gas within the gas mixture may be between approximately 70 percent and approximately 90 percent.

In some embodiments, the gas mixture may consist essentially of the nitrogen precursor and neon. In alternative embodiments, the gas mixture may consist essentially of the nitrogen precursor and helium. In some embodiments, the gas mixture consisting essentially of the nitrogen precursor and helium may be introduced into the reaction chamber at a flow rate ratio of helium to nitrogen precursor greater than 4:1, or greater than 10:1, or greater than 15:1, or even equal to or greater than 20:1. For example, in some embodiments, the gas mixture consisting essentially of the nitrogen precursor and helium may be introduced into the reaction chamber at a flow rate ratio of helium to nitrogen precursor between approximately 4:1 and approximately 20:1. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor and helium and the percent volume content of helium in the gas mixture may be greater than 70 percent, or greater than 80 percent, or even equal to or greater than 85 percent, i.e., a volume ratio of helium (He) to nitrogen precursor of equal to or greater than approximately 6:1.

Not to be bound by any theory or mechanism but it is believed that the addition of an additional gas, such as helium or neon, to the nitrogen precursor results in the generation of a nitrogen based plasma with an increased population density of reactive species such as atomic nitrogen, nitrogen radicals, and/or excited nitrogen species. In addition, when generating a plasma from a gas mixture comprising a nitrogen precursor and the additional gas, the pressure within the reaction chamber may be further increased beyond that commonly utilized in PEALD processes to further increase the population density of reactive species without degradation in the quality of the silicon nitride film deposited. The increase in the population density of reactive species therefore reduces the time period required for the reaction with the absorbed monolayer of silicon species to form the silicon nitride film thereby reducing the plasma exposure time and the overall time period required to deposit a silicon nitride film to a desired thickness, i.e., an increase in the growth rate of a silicon nitride film per unit cycle of the PEALD process.

The difference between a conventional pure nitrogen (N₂) plasma and a plasma generated from a gas mixture comprising a nitrogen precursor and an additional gas is illustrated with reference to FIG. 2A and FIG. 2B. FIG. 2A illustrates the optical emission spectra (OES) taken at various wavelengths with increasing pressure within the reaction chamber. As seen in FIG. 2A, the emission intensity of the OES signal decreases at reaction chamber pressures above 2000 Pascals indicating that the population density of reactive species decreases above a reaction chamber pressure of 2000 Pascals. As a consequence of the decrease in the population density of reactive species above a reaction chamber pressure of 2000 Pascals, the time period required for forming a silicon nitride film utilizing a conventional pure nitrogen (N₂) plasma accordingly increases. In comparison, FIG. 2B illustrates OES spectra at various wavelengths with increasing reaction chamber pressure for a plasma produced from a gas mixture comprising nitrogen (N₂) and helium, wherein the helium volume content is 85%, i.e., a flow rate ratio of He:N₂ of approximately 6:1. Examination of the emission intensity of the OES spectrum taken at a wavelength of 337 nanometers (data labelled 300) clearly illustrates that the emission intensity dramatically increases with increasing reaction chamber pressure corresponding to an increase in the population density of reactive species and a consequently a decrease in the time period required for formation of a silicon nitride film. In addition, examination of the emission intensity of the N₂+ ion optical emission at 391 nanometers (data labelled 302) illustrates that the N₂+ ion population density monotonically decreases with increasing pressure, which indicates that ion bombardment reduces at higher reaction chamber pressures which may in turn prevent ion damage in the deposited silicon nitride film.

In some embodiments of the disclosure, the gas mixture may further comprise argon. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, helium, and argon. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, neon, and argon. As a non-limiting example, a gas mixture consisting essentially of the nitrogen precursor, helium, and argon may be introduced into the reaction chamber continuously throughout the cyclical deposition phase 105 of exemplary PEALD process 100.

In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, helium, and argon, wherein the flow rate ratio of the helium to the nitrogen precursor may be regulated between approximately 4:1 and approximately 20:1 with the addition of a percent content of argon greater than 1%, or greater than 10%, or greater than 20%, or greater than 30%, or greater than 40%, or greater than 50%, or even greater than 60%. For example, the percent content of argon in the gas mixture may be regulated between approximately 1% and approximately 60%.

In some embodiments, a nitrogen based plasma may be produced from the gas mixture comprising a nitrogen precursor and an additional gas. For example, a nitrogen based plasma may be generated by applying RF power from about 10 W to about 2000 W, or from about 50 W to about 1000 W, or from about 100 W to about 500 W. In some embodiments, the plasma may be generated in-situ, while in other embodiments, the plasma may be generated remotely. In some embodiments, a showerhead reactor may be utilized and plasma may be generated between a susceptor (on top of which the substrate is located) and a showerhead plate.

In some embodiments, the reactive species generated from the plasma may contact the substrate for a time period between about 0.1 seconds to about 10 seconds, or about 0.5 seconds to about 5.0 seconds, or even about 0.5 seconds to about 2.0 seconds. In some embodiments, the reactive species generated from the plasma may contact the substrate for a time period of less than 1 second, or less than 0.5 seconds, or even less than 0.1 seconds. In some embodiments, the gas mixture comprising a nitrogen precursor and an additional gas may generate a plasma with a higher population density of reactive species when compared with prior PEALD processes, which may in turn reduce the plasma exposure time required to convert the chemisorbed silicon species to silicon nitride. Therefore, in some embodiments, the reactive species generated from the plasma of the current disclosure may contact the substrate for time period between approximately 0.1 seconds and approximately 1.0 second. However, depending on the reactor type, substrate type and the substrate surface area, the pulsing time for the reactive species may be even greater than about 10 seconds.

After a time period sufficient to completely saturate and react the previously absorbed molecular layer with the nitrogen based plasma pulse, any excess reactant and reaction byproducts may be removed from the reaction chamber. As with the removal of the first reactant, i.e., the vapor phase silicon precursor, this step may comprise stopping generation of reactive species and continuing to flow an inert gas, such as a gas mixture comprising nitrogen, helium, and in some embodiments additionally argon. The inert gas flow may flow for a time period sufficient for excess reactive species and volatile reaction byproducts to diffuse out of and be purged from the reaction chamber. For example, the purge process may be utilized for a time period between about 0.1 seconds to about 10 seconds, or about 0.1 seconds to about 4.0 seconds, or even about 0.1 seconds to about 0.5 seconds. Together, the nitrogen based plasma provision and removal represent a second, reactive species phase in the exemplary silicon nitride PEALD process 100 of FIG. 1.

The method wherein the substrate is alternately and sequentially contacted with the vapor phase silicon precursor and contacted with the reactive species generated from a gas mixture comprising nitrogen and an additional gas may constitute a unit deposition cycle. In some embodiments of the disclosure, the exemplary PEALD process 100 may comprise repeating the unit deposition cycle one or more times. For example, the cyclical deposition stage 105 of exemplary PEALD process 100 may continue with a decision gate 140 which determines if the PEALD process 100 continues or exits. The decision gate of process block 140 is determined based on the thickness of the silicon nitride film deposited, for example, if the thickness of the silicon nitride film is insufficient for the desired device structure, then the PEALD process 100 may return to the process block 120 and the processes of contacting the substrate with the silicon precursor and contacting the substrate with the reactive species (process block 130) may be repeated one or more times. Once the silicon nitride film has been deposited to a desired thickness the exemplary PEALD process 100 may exit by means of a process block 150 and the silicon nitride film may be subjected to additional processes to form a semiconductor device structure.

While the PEALD cycle is generally referred to herein as beginning with the silicon phase, it is contemplated that in other embodiments the cycle may begin with the reactive species phase. One of skill in the art will recognize that the first precursor phase generally reacts with the termination left by the last phase in the previous cycle. Thus, while no reactant may be previously absorbed on the substrate surface or present in the reaction chamber if the reactive species is the first phase in the PEALD cycle, in subsequent cycles the reactive species phase will effectively follow the silicon phase. In some embodiments, one or more different PEALD cycles are provided in the deposition process.

A further overview of a non-limiting exemplary unit deposition cycle of the PEALD processes of the current disclosure is illustrated with reference to FIG. 3. As illustrated in FIG. 3, the x-axis represents time and the y-axis represent the amount of flow of the silicon precursor, the purge gas, the helium and the optional argon. In addition, the y-axis for the RF plasma represents the off-state and the on-state, i.e., the application of RF power to the gas mixture. In brief, the purge flow may be continuous throughout a unit deposition cycle and in addition the helium flow and the optional argon flow may also be continuous throughout a unit deposition cycle. In contrast, the silicon precursor may introduced into the reaction chamber as a discrete pulse of vapor phase reactant and the RF plasma may be applied as a discrete pulse of RF power generating a discrete pulse of reactive species. Both the silicon precursor pulse and RF plasma pulse may be followed by a subsequent purging step to remove excess reactant, reactive species, and reactant byproducts.

In some embodiments, the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process may be greater than 0.035 nanometers per cycle at a substrate temperature of less than 450° C. In some embodiments, the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process maybe greater than 0.027 nanometers per cycle at a substrate temperature of less than 350° C. In some embodiments, the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process may be greater than 0.024 nanometers per cycle at a substrate temperature of less than 250° C. In some embodiments of the disclosure, the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process may be between about 0.024 nanometers per cycle and 0.035 nanometers per cycle.

In some embodiments, the silicon nitride films of the current disclosure may be deposited to a thickness from about 3 nanometers to about 50 nanometers, or from about 5 nanometers to about 30 nanometers, or from about 5 nanometers to about 20 nanometers. These thicknesses may be achieved in feature sizes (width) below about 100 nanometers, or below about 50 nanometers, or below about 30 nanometers, or below about 20 nanometers, or even below about 10 nanometers.

In some embodiments of the disclosure, the silicon nitride film may be deposited on a three-dimensional structure, e.g., a non-planar substrate comprising high aspect ratio features. In some embodiments, the step coverage of the silicon nitride film may be equal to or greater than about 50%, or greater than about 60%, or greater than 70%, or greater than 80%, or greater than about 90%, or greater than about 95%, or greater than about 98%, or greater than about 99%, or greater in structures having aspect ratios (height/width) of more than about 2, more than about 5, more than about 10, more than about 25, more than about 50, or even more than about 100.

In some embodiments, the silicon nitride films deposited according the PEALD processes disclosed herein may have superior etch resistance to comparable silicon nitride films deposited by prior plasma-enhanced deposition processes. For example, the ratio of a wet etch rate of the silicon nitride films deposited by the PEALD processes of the disclosure relative to a wet etch rate of thermal silicon oxide (WERR) in dilute hydrofluoric acid (1:100) may be less 1.0, or less than 0.5, or less than 0.35, or less than 0.20, or less than 0.15, or between approximately 1.0 and approximately 0.15.

In some embodiments, the ratio of the wet etch rate of the silicon nitride films deposited by the PEALD processes of the disclosure relative to a wet etch rate of thermal silicon oxide (WERR) in dilute hydrofluoric acid (1:100) may be improved by depositing the silicon nitride film at increased reaction chamber pressure.

In more detail, FIG. 4 illustrates the WERR (vs thermal oxide in dilute hydrofluoric acid (1:100)) of various silicon nitride films deposited utilizing a plasma generated from a gas mixture comprising nitrogen (N₂) and helium (data labelled 400) and utilizing a plasma generated from a gas mixture comprising nitrogen (N₂), helium, and argon (data labelled 402). Examination of FIG. 4 illustrates that the WERR (vs thermal oxide in dilute hydrofluoric acid (1:100)) of the silicon nitride films deposited according to the embodiments of the current disclosure dramatically improves above a reaction chamber pressure of approximately 3000 Pascals for both N₂/He based plasmas and N₂/He/Ar based plasmas. Therefore, in some embodiments of the disclosure, the silicon nitride films of the current disclosure may be deposited utilizing at least one unit deposition cycle of a PEALD process at a reaction chamber pressure greater than approximately 3000 Pascals, or greater than approximately 400 Pascals, or greater than approximately 5000 Pascals, or between a pressure range of approximately 3000 Pascals to approximately 5000 Pascals. In such embodiments wherein the silicon nitride films are deposited above a reaction chamber pressure of 3000 Pascals the WERR (vs thermal oxide in dilute hydrofluoric acid (1:100) of the silicon nitride films deposited according to the embodiments of the disclosure may be less than 1.0, or less than 0.5, or less than 0.35, or less than 0.20, or even less than 0.15.

Not to be bound by any theory or mechanisms but it is proposed that as the reaction chamber pressure is regulated above 3000 Pascals, or regulated between 3000 Pascals and 5000 Pascals, the ion bombardment (e.g., by N₂+ ions) of the deposited silicon nitride film may decrease, not only due to the short mean free path of ions but also due to a lower population density of ions (as discussed with reference to FIG. 3B). The decrease in ion bombardment of the silicon nitride films of the current disclosure above a reaction chamber pressure of 3000 Pascals may in turn result in silicon nitride films of higher quality due to a decrease in damage from ion bombardment.

In some embodiments the SiN films deposited according to PEALD processes described herein may have a Si:N ratio of ranging between 42-48:52-58. In some embodiments, the silicon nitride films deposited according to the embodiments of the disclosure may have a density between approximately 2.0 g/cm³ and approximately 3.1 g/cm³. In some embodiments, the silicon nitride films deposited according to the embodiments of the disclosure may have a refractive index between approximately 1.8 and approximately 2.0.

Additional embodiments of the disclosure may include further methods for forming a silicon nitride film which may include a post deposition plasma treatment which may be utilized to improve the wet etch rate uniformity of a silicon nitride film.

Prior PEALD processes may deposit a SiN film over a substrate with high aspect ratio features with anisotropic SiN film properties. For example, the high aspect ratio features on the substrate may comprise high aspect ratio trenches including vertical portions and lateral portions and the SiN film disposed over vertical portions may have a different wet etch rate to the SiN film disposed over the lateral portions of the trenches. The difference in wet etch rate between lateral portions of the SiN film and vertical portions of the SiN may be due in part to the directionality of the reactive species generated by the plasma in the PEALD processes.

In comparison, the embodiments of the current disclosure may form SiN films over high aspect ratio features, such as trench structures including vertical portions and lateral portions, wherein the SiN film has a more uniform wet etch rate between the SiN film disposed over the vertical portions and SiN film disposed over the lateral portions. In addition to forming SiN films with improved wet etch uniformity, the embodiments of the disclosure may also lower the wet etch rate of the SiN films, which may be advantageous in process applications wherein the SiN films are utilized as etch masks. The embodiments of the disclosure may achieve the improvements in the etch characteristics of a silicon nitride film by exposing a silicon nitride film post-deposition to a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, such as, for example, helium or neon.

Therefore the embodiments of the disclosure may include methods for forming a silicon nitride film, the method comprising: providing a substrate into a reaction chamber; depositing a silicon nitride film on a surface of the substrate; and contacting the silicon nitride film with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.

In more detail, FIG. 5 illustrates an exemplary process 500 for forming a silicon nitride film. The exemplary process 500 may commence by means of a process block 510 comprising, providing a substrate into a reaction chamber and heating to a deposition temperature. The process block 510 may be substantially the same as the process block 110 of FIG. 1 and is therefore not described in further detail with reference to exemplary process 500.

The exemplary process 500 may continue by means of a process block 520 comprising, depositing a silicon nitride film on a surface of a substrate. In some embodiments, the silicon nitride film may deposited be a PEALD process by performing at least one unit deposition cycle of a PEALD process, such as exemplary PEALD process 100 of FIG. 1. In some embodiments of the disclosure, the silicon nitride film may be deposited by alternative PEALD processes or thermal atomic layer deposition processes, examples of which may be found in more detail in U.S. Pat. No. 9,564,309, filed on Jan. 29, 2014, entitled SI PRECURSORS FOR DEPOSITION OF SIN AT LOW TEMPERATURES, all of which is hereby incorporated by reference and made a part of this specification.

Once the silicon nitride film has been deposited to a desired thickness, the exemplary process 500 may continue by means of a process block 530 comprising: contacting the silicon nitride film with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to the nitrogen precursor greater than 4:1.

In more detail, the post deposition plasma treatment of process block 530 may comprise controlling the temperature of the substrate to less than 550° C., or less than 400° C., or less than 300° C., or less than 200° C., or less than 100° C., or even less than 50° C. For example, during the post deposition plasma treatment the substrate may be controlled between a temperature of approximately 25° C. and approximately 550° C.

In addition to controlling the temperature of the substrate, the pressure within the reaction chamber may also be regulated during the post deposition plasma treatment. For example, the pressure in the reaction chamber may be regulated at greater than 2000 Pascals, or greater than 3000 Pascals, or greater than 4000 Pascals, or greater than 5000 Pascals, or even greater than 6000 Pascals. In certain embodiments, the pressure in reaction chamber may be regulated during the post deposition plasma treatment between approximately 2000 Pascals and approximately 6000 Pascals.

In some embodiments, the post deposition plasma treatment may employ a nitrogen based plasma produced from a gas mixture comprising a nitrogen precursor and an additional precursor. In some embodiments, the nitrogen precursor may comprise at least one of nitrogen (N₂), ammonia (NH₃), hydrazine (N₂H₄), or an alkyl-hydrazine (e.g., tertiary butyl hydrazine (C₄H₁₂N₂). In some embodiments, the additional gas may comprise at least one of helium or neon and the gas mixture may be introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen gas greater than 4:1, or greater than 10:1, or greater than 15:1, or even equal to or greater than 20:1. In some embodiments, the flow rate ratio of the additional gas to nitrogen precursor into the reaction chamber may be between approximately 4:1 and approximately 20:1. For example, the percentage volume of the additional gas within the gas mixture may be greater than 70 percent, or greater than 75 percent, or greater than 80 percent, or greater than 85 percent, or even greater than 90 percent.

In some embodiments, the gas mixture may consist essentially of the nitrogen precursor and neon. In alternative embodiments, the gas mixture may consist essentially of the nitrogen precursor and helium. In some embodiments, the gas mixture consisting essentially of the nitrogen precursor and helium may be introduced into the reaction chamber at a flow rate ratio of helium to nitrogen precursor greater than 4:1, or greater than 10:1, or greater than 15:1, or even equal to or greater than 20:1. For example, in some embodiments, the gas mixture consisting essentially of the nitrogen precursor and helium may be introduced into the reaction chamber at a flow rate ratio of helium to nitrogen precursor between approximately 4:1 and approximately 20:1. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor and helium and the percent volume content of helium in the gas mixture may be greater than 70 percent, or greater than 80 percent, or even equal to or greater than 85 percent, i.e., a volume ratio of helium (He) to nitrogen precursor of equal to or greater than approximately 6:1.

In some embodiments of the disclosure, the gas mixture may further comprise argon. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, helium, and argon. In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, neon, and argon.

In some embodiments, the gas mixture may consist essentially of the nitrogen precursor, helium, and argon, wherein the flow rate ratio of the helium to the nitrogen precursor may be regulated between approximately 4:1 and approximately 20:1 with the addition of a percent content of argon greater than 1%, or greater than 10%, or greater than 20%, or greater than 30%, or greater than 40%, or greater than 50%, or even greater than 60%. For example, the percent content of argon in the gas mixture may be regulated between approximately 1% and approximately 60%.

In some embodiments, a nitrogen based plasma may be produced from the gas mixture comprising a nitrogen precursor and an additional gas. For example, a nitrogen based plasma may be generated by applying RF power from about 10 W to about 2000 W, or from about 50 W to about 1000 W, or from about 100 W to about 500 W. In some embodiments, the plasma may be generated in-situ, while in other embodiments, the plasma may be generated remotely. In some embodiments, a showerhead reactor may be utilized and plasma may be generated between a susceptor (on top of which the substrate is located) and a showerhead plate.

In some embodiments, the nitrogen based plasma may contact the silicon nitride film for time period of less than 300 seconds, or less than 150 seconds, or less 100 seconds, or less 50 seconds, or less than 25 seconds, or even less than 5 seconds. For example, the nitrogen based plasma may contact the silicon nitride film for a time period between approximately 5 seconds and approximately 300 seconds.

Once the post-deposition plasma treatment has been completed the reaction chamber may be purged of excess reactant and any reactant byproduct and the exemplary process 500 may exit by means of a process block 540 and the substrate with the silicon nitride film thereon may be subjected to further semiconductor processing methods for forming a semiconductor device structure.

In some embodiments of the disclosure, the silicon nitride treated with the post deposition plasma treatment may have wet etch rate in dilute hydrofluoric acid (1:100) of less than 0.3 nanometers per minute, or less than 0.2 nanometers per minute, or even less than 0.1 nanometers per minute. As a non-limiting example embodiments, the silicon nitride film may be deposited by repeated unit cycles of the PEALD processes of the current disclosure and subsequent exposed to the post deposition plasma treatment to produce a silicon nitride film with wet etch rate in dilute hydrofluoric acid (1:100) of less than 0.3 nanometers per minute, or less than 0.2 nanometers per minute, or even less than 0.1 nanometers per minute

In some embodiments of the disclosure, the silicon nitride film may be deposited over a gap feature and the silicon nitride film may be disposed over a lateral portion of the gap feature and disposed and over a sidewall portion of the gap feature, wherein the percentage difference in the wet etch ratio (WERR) in dilute hydrofluoric acid (1:100) of the silicon nitride film disposed over the lateral portion compared with the (WERR) of the silicon nitride film disposed over the sidewall portion is less than 66 percent, or less than 50 percent, or less than 40 percent, or less than 30 percent, or less than 20 percent, or even less than 10 percent.

The example embodiments of the disclosure described above do not limit the scope of the invention, since these embodiments are merely examples of the embodiments of the invention, which is defined by the appended claims and their legal equivalents. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the disclosure, in addition to those shown and described herein, such as alternative useful combination of the elements described, may become apparent to those skilled in the art from the description. Such modifications and embodiments are also intended to fall within the scope of the appended claims. 

What is claimed is:
 1. A method for forming a silicon nitride film by a plasma enhanced atomic layer deposition (PEALD) process, the method comprising: providing a substrate into a reaction chamber; and performing at least one unit deposition cycle of a PEALD process, wherein a unit cycle comprises: contacting the substrate with a vapor phase reactant comprising a silicon precursor; and contacting the substrate with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 4:1.
 2. The method of claim 1, wherein the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 10:1.
 3. The method of claim 1, wherein the gas mixture is introduced into the reaction chamber at a flow rate ratio of additional gas to nitrogen precursor greater than 15:1.
 4. The method of claim 1, further comprising regulating the pressure within the reaction chamber during the PEALD process to greater than 3000 Pascals.
 5. The method of claim 1, wherein the gas mixture consists essentially of the nitrogen precursor and helium.
 6. The method of claim 1, wherein the gas mixture further comprises argon.
 7. The method of claim 6, wherein the gas mixture consists essentially of the nitrogen precursor, helium, and argon.
 8. The method of claim 6, wherein the silicon nitride film has a wet etch rate ratio (WERR) in dilute hydrofluoric acid (1:100) of less than 0.15.
 9. The method of claim 1, wherein the nitrogen precursor comprises at least one of nitrogen (N₂), ammonia (NH₃), hydrazine (N₂H₄), or an alkyl-hydrazine.
 10. The method of claim 1, wherein the silicon precursor comprises a silicon halide precursor.
 11. The method of claim 10, wherein the silicon halide precursor comprises at least one of a silicon chloride precursor, a silicon iodide precursor, or a silicon bromide precursor.
 12. The method of claim 11, wherein the silicon iodide precursor comprises at least one of HSiI₃, H₂SiI₂, H₃SiI, H₂Si₂I₄, H₄Si₂I₂, or H₅Si₂I.
 13. The method of claim 1, further comprising contacting the substrate with the reactive species for a time period of less than 1 second.
 14. The method of claim 1, wherein the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process is greater than 0.035 nanometers per cycle at a substrate temperature of less than 450° C.
 15. The method of claim 1, wherein the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process is greater than 0.027 nanometers per cycle at a substrate temperature of less than 350° C.
 16. The method of claim 1, wherein the growth rate of the silicon nitride film per unit deposition cycle of the PEALD process is greater than 0.024 nanometers per cycle at a substrate temperature of less than 250° C.
 17. The method of claim 1, wherein the silicon nitride film has a wet etch rate ratio (WERR) in dilute hydrofluoric acid (1:100) of less than 0.35.
 18. The method of claim 1, further comprising contacting the silicon nitride film post-deposition with a reactive species generated from a plasma produced from a gas mixture comprising a nitrogen precursor and an additional gas, wherein the additional gas comprises at least one of helium or neon and the gas mixture comprises a percentage volume content of the additional gas greater than 70 percent. 